1. Technical Field
The present invention relates to a method for reducing the content of siloxane oligomer which is present in organopolysiloxane moldings.
2. Prior Art
Organopolysiloxane moldings consist of moldings made of silicone resins, as well as, moldings made of silicone rubbers such as heat-vulcanizing silicone rubbers, silicone rubbers which cure at room temperature under the influence of moisture, and addition reaction-curing silicone rubbers. These assume a large number of configurations in accordance with the particular application, such as films, sheets, plates, massive or bulk configurations, spherical forms, microparticulate configurations, laminates, and so forth. Regardless of the nature of the curing reaction, these moldings typically contain some level of siloxane oligomer. It has become clear that this siloxane oligomer exercises adverse effects in a wide variety of the applications of these moldings, and demand has arisen for the removal of this siloxane oligomer.
Evaporative procedures are the most common prior art methods for the removal of the siloxane oligomer in organopolysiloxane moldings. These have consisted of removing the siloxane oligomer by executing a high-temperature stripping treatment in vacuo at the level of the organopolysiloxane prior to production of the molding.
For example, Japanese Patent Application Laid Open [Kokai or Unexamined] Number 63-44681 [44,681/88], published Feb. 25, 1988, discloses a silicone rubber fixer roll which contains less than 0.2 weight % low-molecular-weight siloxane with vapor pressure .gtoreq.10 mmHg at 200.degree. C. This is achieved by an in vacuo heat treatment of the organopolysiloxane prior to molding.
Zosel in U.S. Pat. No. 3,969,196, issued Jul. 13, 1976, teaches a method of separating various mixtures of organic compounds in liquid or solid state by contacting the mixture with a gas maintained under supercritical conditions of temperature and pressure, separating the gas in the form of an identifiable gas phase loaded with a compound taken up during contact of the mixture by the gas, and thereafter separating the compound from the gas.